The present invention relates to a level detector to detect the level of a liquid. More particularly, the present invention relates to such a level detector in which an intermediate temperature of an unwetted length of an elongated probe is sensed to determine the height of the liquid level.
The prior art has provided a variety of devices that are used to sense the level of a liquid. Common level detectors use electrical capacitance measurements or hydrostatic pressure to measure the continuous level of a liquid. There are also point level detectors. In U.S. Pat No. 5,167,154, invented by the inventor herein, a thermal conductor sheathed in an insulator is provided to conduct heat from the ambient to a distal, sensing end of the device. At the distal end of the thermal conductor, a thermocouple is provided to sense temperature. Since the liquid has a greater convective heat transfer coefficient than the vapor phase of the liquid overlying the liquid, upon submergence of the distal end of the probe, the temperature will decrease in proportion to the increase in the heat transfer coefficient. This will result in a decrease in temperature sensed by the thermocouple which can be interpreted as the liquid reaching the point or distal end of the probe.
Point level detectors do not, however, sense the actual height of the liquid level above a reference point. As will be discussed, the present invention provides a level detector to detect the height of a liquid level.